The present invention relates to a fuel cell, and particularly to a fuel cell of manifold type.
A fuel cell is in such a structure as to supply and discharge fuel and an oxidizing agent, for example, air. According to an inside passage type, one type of the fuel cell, a common passage for supplying and discharging a gas is provided in an electrode, but such type has a complicated electrode structure, often making gas distribution to a gas reaction part uneven, and is substantially not applicable to a large fuel cell. Thus, a fuel cell of manifold type, in which gas supply and discharge are carried out through manifolds provided at four sides of a stacked fuel cell, has been recently used as a large fuel cell.
One example of the conventional fuel cell of manifold type will be outlined below, referring to drawings.
In FIG. 1 showing a schematic cutaway view of members constituting a fuel cell, FIG. 2 showing a schematic view of a stacked state of the members of FIG. 1, and FIG. 3 showing a partial cutaway plan view of a stacked fuel cell in a housing tank, a fuel electrode plate 1 and an air electrode plate 2 are comprised of graphite fibers, and are each provided with a large number of ribs on one side thereof, forming a gas passage 3. At the flat side opposite to the ribbed side is provided a catalyst layer 4 prepared, for example, by coating graphite powder containing diffused platinum powder thereon. The fuel electrode plate 1 and the air electrode plate 2 are stacked through a matrix 5 for retaining an electrolyte solution, for example, a phosphoric acid solution so that the flat sides can be tightly secured face-to-face, and the gas passages 3 provided on the electrode plates can be crossed on one electrode plate to another to form a unit cell. The thus arranged unit cells are stacked through separators 6 for fuel and air. A cooler 7 is also a ribbed plate provided with cooling tubes 8 between the ribs, and is provided for a predetermined number of the unit cells. Both end of each cooling tube 8 are connected to an inlet main pipe 11 and an outlet main pipe through an inlet branch pipe 9 and an outlet branch pipe 10.
Manifolds 13 are provided at four sides of the thus stacked assembly 14 to form spaces for supplying and discharging gases, and are also provided with gas supply pipes 15a and 15b and gas discharge pipes 16a and 16b through the housing tank 17 to permit gas supply and discharge from the outside of the housing tank 17. A cooling water supply pipe 18 and a cooling water discharge pipe 19 are connected to the inlet main pipe 11 and the outlet main pipe 12, respectively, in the manifold 13 through the housing tank 17 and the manifold 13.
A hydrogen gas as fuel is supplied to the fuel cell having the foregoing structure through the gas supply pipe 15a in the direction of full arrow line as in FIG. 3, and air through the gas supply pipe 15b in the direction of dotted arrow line to generate electric current by electrochemical reaction at the catalyst layers.
However, gas sealing of the fuel cell of such manifold type is effected only by tight sealing between the edge parts of the manifolds 13 and the edge parts at the four sides of the stacked assembly 14, and thus very high precision is required for dimensioning of the four sides. Furthermore, the cooling water pipings must be provided in the manifold, so that the structure of fuel cell is very complicated and its fabrication is not made easily. There is also a possibility of contact of the cooling water pipings with the vapor of phosphoric acid used as the electrolyte, with consequent restriction to the materials of construction of the cooling water piping. These are the disadvantages of the conventional fuel cell of manifold type.